Recently, cutting tools such as inserts and end mills, in which cBN sintered material is used in the cutting edge part, are provided as a tool for machining molds used for manufacturing housings of the cellular phones, the smart phones, or the like. The cBN sintered material exhibits high productivity and long service life; and has a highest hardness next to diamonds.
However, the cBN sintered material itself is hard to be machined, and expensive. Furthermore, usage of the cBN sintered material is restricted since the shape of sintered material is limited to discoid shapes and the tool shape cannot be formed freely.
Despite the difficulty of machining tools, there are growing applications of the cBN sintered material recently with increase of the amount of difficult-to-cut materials. As a method to overcome the problems of the production cost and workability, a cutting tool is proposed. In the cutting tool, a cutting tool body made of WC-based cemented carbide; and a cutting edge part, the material of which is the cBN sintered material, are bonded by brazing the cutting tool body made of WC-based cemented carbide, which is inexpensive and has excellent workability, and the cutting edge part, the material of which is the cBN sintered material. In addition, not only the cBN sintered materials, but several technologies relating to composite parts made of the cutting tool body made of the WC-based cemented carbide and other material are proposed.
For example, a technology is proposed in Japanese Unexamined Patent Application, First Publication No. H11-320218 (A), in which the cBN sintered material is bonded to the cutting tool body made of WC-based cemented carbide strongly by forming a bonding part made of: one or more of Ti and Zr at 15 to 65 weight %; and Cu without occurrence of splitting or cracking of the cBN sintered material in a cutting tool in which the cBN sintered material is bonded on the cutting tool body made of WC-based cemented carbide through the bonding part.
In addition, improvement of the bonding strength between the cemented carbide part and the steel part is described Japanese Unexamined Patent Application, First Publication No. 2009-131917 (A). Japanese Unexamined Patent Application, First Publication No. 2009-131917 (A) relates to: the composite material of a cemented carbide part and a steel part, in which the cemented carbide part and the steel part are bonded through a bonding layer; and a cutting tool such as end mills, drills, and the like, on which cutting edge processing is performed to the cemented carbide part of the composite material. The bonding strength between the cemented carbide part and the steel part is improved: by having the bonding layer made of Ni on the side contacting the cemented carbide part; by having the bonding layer made of the Ni—Cu alloy on the side contacting the steel part; and by forming the Cu diffusing region, in which the Cu content reduces with distance from the bonding surface, in the vicinity of the bonding surface between the steel part and the bonding layer.
In addition, it is proposed that cutting blade having less residual stress and high bonding strength can be obtained: by bonding the blade part made of cemented carbide and the body part made of carbon tool steel through the nickel or cobalt foil; by irradiating laser on the bonding part; and bonding the blade part and the body part through the alloy layer, in Japanese Unexamined Patent Application, First Publication No. 2008-100348 (A).
In addition, improvement of bonding strength between the cBN-based sintered material and the cutting tool body made of WC-based cemented carbide is disclosed in Japanese Unexamined Patent Application, First Publication No. 2012-111187 (A). In Japanese Unexamined Patent Application, First Publication No. 2012-111187 (A), the cBN-based sintered material is bonded on the cutting tool body made of WC-based cemented carbide through the bonding part. In addition, the titanium nitride compound layer having the layer thickness of 10 nm to 300 nm is formed in the interface between the cBN-based sintered material and the bonding part; and the layer thickness of the bonding part on the back surface of the cBN-based sintered material is thinner than the layer thickness of the bonding part on the bottom surface.